Influence of synthesis route and Ce/Zr ratio on the structural and nanostructure properties of Ce–Zr–O mixed oxides

Abstract

Ceria–zirconia (CeO₂–ZrO₂, CZ) solid solutions, noted for excellent oxygen storage capacity (OSC), high thermal stability, and uses in three-way catalysts, solid oxide fuel cells, and sensors. Ce–Zr–O mixed oxides were synthesized by solid-state reaction and hydrothermal routes, and the effects of synthesis pathway, Ce/Zr ratio, and hydrothermal holding time on phase formation and textural properties were quantitatively examined. Solid-state synthesis followed by sintering at 1620 °C and annealing at 600 °C produced a single-phase tetragonal Ce₀.₅Zr₀.₅O₂ solid solution with a BET surface area of 0.47 m² g⁻¹, average pore diameter of 23.4 nm, and total pore volume of 0.0027 cm³ g⁻¹. Hydrothermal synthesis at 100 °C for 10–48 h and calcination at 400 °C yielded nanocrystalline fluorite-type Ce_1-xZr_xO₂ solid solutions with crystallite sizes below 10 nm. Depending on composition and holding time, BET surface areas ranged from 6.0 to 75.1 m² g⁻¹. The highest surface area (75.1 m² g⁻¹) was obtained for Ce₀.₅Zr₀.₅O₂ synthesized for 10 h, decreasing to 69.4 and 59.2 m² g⁻¹ after 24 and 48 h, respectively. For Ce₀.₂₅Zr₀.₇₅O₂, the maximum surface area (24.7 m² g⁻¹) occurred at 24 h, while Ce₀.₅₇Zr₀.₄₃O₂ samples exhibited surface areas of 50.4–62.2 m² g⁻¹. Nitrogen adsorption–desorption isotherms of hydrothermal samples correspond to type IV with average pore diameters of 3.9–29 nm. FESEM analysis showed hierarchical aggregates composed of 20–40 nm primary nanoparticles.